\n\n[](https://discord.com/invite/b5rXHjAg7A)\n[](https://clerk.dev/docs?utm_source=github&utm_medium=clerk_backend_core)\n[](https://twitter.com/intent/follow?screen_name=ClerkDev)\n\n[Changelog](https://github.com/clerkinc/javascript/blob/main/packages/backend-core/CHANGELOG.md)\n·\n[Report a Bug](https://github.com/clerkinc/javascript/issues/new?assignees=&labels=bug&template=bug_report.md&title=Bug%3A+)\n·\n[Request a Feature](https://github.com/clerkinc/javascript/issues/new?assignees=&labels=enhancement&template=feature_request.md&title=Feature%3A+)\n·\n[Ask a Question](https://github.com/clerkinc/javascript/issues/new?assignees=&labels=question&template=ask_a_question.md&title=Support%3A+)\n\n
\n\n---\n\n## Overview\n\nThis package provides Clerk Backend API core resources and low-level authentication utilities for JavaScript environments. It is mostly used as the base for other Clerk SDKs.\n\n## Getting Started\n\n### Installation\n\n```sh\nnpm install @clerk/backend-core\n```\n\n### Build\n\nTo build the package locally with the TypeScript compiler, run:\n\n```sh\nnpm run build\n```\n\n## Architecture\n\n`@clerk/backend-core` contains all the logic for basic Clerk functionalities, without being platform/environment, specific such as:\n\n- Determining the authentication state of a session.\n- Validating a Clerk token state.\n- Clerk API resource management.\n\n### How it works\n\nThis package is used as the base building block for Clerk JavaScript SDKs and environments. This is achieved by providing all the required business logic if only a few environment-specific utilities are implemented by the client.\n\n
\n\nIn essence, the client should supply these key functions in the Clerk [Base](./src/Base.ts#47) and [ClerkBackendApi](./src/api/ClerkBackendApi.ts) classes:\n\n1. Public key import `importKeyFunction`.\n2. JWT signature verification `verifySignatureFunction`.\n3. Base64 decoding `decodeBase64Function`.\n4. HTTP fetching utility for the API resource management `ClerkFetcher`.\n\nAfter supplying those in the `Base` and `ClerkBackendApi` classes, you can use all the Clerk utilities required for the SDK business logic.\n\n## Usage\n\n### Creating a Base for a new SDK\n\n```ts\nconst importKey = async (jwk: JsonWebKey, algorithm: Algorithm) => {\n // ...\n};\n\nconst verifySignature = async (algorithm: Algorithm, key: CryptoKey, signature: Uint8Array, data: Uint8Array) => {\n // ...\n};\n\nconst decodeBase64 = (base64: string) => {\n // ...\n};\n\n/** Base initialization */\nconst examplePlatformBase = new Base(importKey, verifySignature, decodeBase64);\n```\n\nAfter creating the `Base` instance you can use core functions such as:\n\n```ts\nexamplePlatformBase.verifySessionToken(...);\n\nexamplePlatformBase.getAuthState(...);\n```\n\nThe `Base` utilities include the building blocks for developing any extra logic and middleware required for the target platform.\n\n### Validate the Authorized Party of a session token\n\nClerk's JWT session token, contains the azp claim, which equals the Origin of the request during token generation. You can provide a list of whitelisted origins to verify against, during every token verification, to protect your application of the subdomain cookie leaking attack. You can find an example below:\n\n```ts\nconst authorizedParties = ['http://localhost:3000', 'https://example.com'];\n\nexamplePlatformBase.verifySessionToken(token > { authorizedParties });\n```\n\n### Clerk API Resources\n\nAPI resource management is also provided by this package through the [ClerkBackendApi](./src/api/ClerkBackendApi.ts) class. For more information on the API resources you can checkout the [resource documentation page](https://reference.clerk.dev/reference/backend-api-reference).\n\nTo use the Clerk Backend API wrapper in any JavaScript platform, you would need to provide some specific SDK information and an HTTP fetching utility. See more at the [ClerkBackendAPIProps](./src/api/ClerkBackendApi.ts#17) implementation.\n\n## Support\n\nYou can get in touch with us in any of the following ways:\n\n- Join our official community [Discord server](https://discord.com/invite/b5rXHjAg7A)\n- Open a [GitHub support issue](https://github.com/clerkinc/javascript/issues/new?assignees=&labels=question&template=ask_a_question.md&title=Support%3A+)\n- Contact options listed on [our Support page](https://clerk.dev/support?utm_source=github&utm_medium=clerk_backend_core)\n\n## Contributing\n\nWe're open to all community contributions! If you'd like to contribute in any way, please read [our contribution guidelines](https://github.com/clerkinc/javascript/blob/main/packages/backend-core/docs/CONTRIBUTING.md).\n\n## Security\n\n`@clerk/backend-core` follows good practices of security, but 100% security cannot be assured.\n\n`@clerk/backend-core` is provided **\"as is\"** without any **warranty**. Use at your own risk.\n\n_For more information and to report security issues, please refer to our [security documentation](https://github.com/clerkinc/javascript/blob/main/packages/backend-core/docs/SECURITY.md)._\n\n## License\n\nThis project is licensed under the **MIT license**.\n\nSee [LICENSE](https://github.com/clerkinc/javascript/blob/main/packages/backend-core/LICENSE) for more information.\n","engines":{"node":">=14"},"gitHead":"46a7fba0a26b045da091205c34c3aaf54a60ac8d","license":"MIT","scripts":{"dev":"tsc -p tsconfig.esm.json --watch","test":"jest","build":"tsc -p tsconfig.esm.json && tsc -p tsconfig.cjs.json && ./moduleTypeFix"},"_npmUser":{"name":"nikosdouvlis","email":"nikosdouvlis@gmail.com"},"homepage":"https://clerk.dev/","deprecated":"This package has been deprecated - use @clerk/backend instead","repository":{"url":"git+https://github.com/clerkinc/javascript.git","type":"git"},"_npmVersion":"lerna/4.0.0/node@v16.15.0+arm64 (darwin)","description":"Clerk Backend API core resources and authentication utilities for JavaScript environments.","directories":{},"maintainers":[{"name":"giannis-clerk","email":"giannis@clerk.dev"},{"name":"igneel64","email":"p.perlepes@gmail.com"},{"name":"chanioxaris","email":"haris@clerk.dev"},{"name":"agis-clerk","email":"agis@clerk.dev"},{"name":"colinclerk","email":"colin@clerk.dev"},{"name":"bradenclerk","email":"braden@clerk.dev"},{"name":"sokratis","email":"sokratis.vidros@gmail.com"},{"name":"yourtallness","email":"mark@clerk.dev"},{"name":"nikosdouvlis","email":"nikosdouvlis@gmail.com"}],"_nodeVersion":"16.15.0","dependencies":{"tslib":"^2.3.1","node-fetch":"^2.6.0","@types/node":"^16.11.55","@clerk/types":"^3.5.0-staging.4","query-string":"^7.0.1","snakecase-keys":"^5.1.2","@types/node-fetch":"^2","@peculiar/webcrypto":"^1.4.0"},"publishConfig":{"access":"public"},"_hasShrinkwrap":false,"readmeFilename":"README.md","devDependencies":{"jest":"^27.4.7","nock":"^13.2.1","ts-jest":"^27.1.3","typescript":"^4.6.4","@types/jest":"^27.4.0"},"_npmOperationalInternal":{"tmp":"tmp/backend-core_2.4.2-staging.4_1663241975274_0.5096140245353429","host":"s3://npm-registry-packages"},"_id":"@clerk/backend-core@2.4.2-staging.4","version":"2.4.2-staging.4"}
![\"Clerk](\"https://images.clerk.dev/static/clerk.svg\")
\n \n ![](\"https://images.clerk.dev/static/backend_api_architecture.png\")
\n \n